The present invention relates to apparatus used to emboss paper products, preferably elongate webs used to make paper goods, e.g., paper towels, toilet tissue, or paper napkins. Embossing is the act of mechanically working a substrate to cause the substrate to conform under pressure to the depths and contours of a patterned embossing roll. Generally, the web is passed between a pair of emboss rolls that, under pressure, form contours within the surface of the paper.
In most configurations at least one of the two roller surfaces directly carries the pattern to be transferred to the paper web. Known configurations include rigid-to-resilient embossing and rigid-to-rigid embossing.
In a rigid-to-resilient embossing system, a single or multi-ply substrate is passed through a nip formed between a roll whose substantially rigid surface contains the embossing pattern as a multiplicity of protuberances and/or depressions arranged into an aesthetically-pleasing manner, and a second, roll, whose substantially resilient surface can be either smooth or also contain a multiplicity of protuberances and/or depressions which cooperate with the rigid surfaced patterned roll. Commonly, rigid rolls are formed with a steel body which is either directly engraved upon or which can contain a hard rubber-covered surface (directly coated or sleeved) upon which the embossing pattern is laser engraved. The resilient roll may consist of a steel core directly covered or sleeved with a resilient material such as rubber. The rubber coating may be either smooth or engraved with a pattern. The pattern on the resilient roll may be either a mated or a non-mated pattern with respect to the pattern carried on the rigid roll.
In the rigid-to-rigid embossing process, a single-ply or multi-ply substrate is passed through a nip formed between two substantially rigid rolls. The surfaces of both rolls contain the pattern to be embossed as a multiplicity of protuberances and/or depressions arranged into an aesthetically-pleasing manner where the protuberances and/or depressions in the second roll cooperate with those patterned in the first rigid roll. The first rigid roll may be formed, for example, with a steel body which is either directly engraved upon or which can contain a hard rubber-covered surface (directly coated or sleeved) upon which the embossing pattern is laser engraved. The second rigid roll can be formed with a steel body or can contain a hard rubber covered surface (directly coated or sleeved) upon which a matching or mated pattern is conventionally engraved or laser-engraved.
Prior art embossing systems where the embossing pattern is carried directly by one or both of the embossing rolls suffer from a number of disadvantages. Specifically, if the emboss pattern gets damaged or if the pattern becomes fouled with, for example, foreign matter, the emboss process must be interrupted while the roll is cleaned or repaired. Another emboss roll may need to be installed if, for example, the roll is damaged to a point that the pattern must be reground or retooled.
Expense can also be a significant factor in processes requiring a periodic change in the embossing pattern. Such periodic changes can be very expensive if the pattern is applied directly to the roll, since any change in pattern requires that a completely new roll be installed. Installation of a new roll requires that the converting operation be shut down for a time sufficient to complete the roll change. As discussed above, the amount of time that the converting line must be shut down can have a significant impact on productivity, and thereby cost.
Other problems with typical prior art rolls include uneven wear patterns on the emboss rolls. These uneven patterns either require that the roll be replaced and reground or that for a period of time the converting operation be continued with emboss definition in the cross-machine direction of the web which is uneven and/or unreliable.
Thus, there is an advantage to a system having emboss pattern elements that are not integral with the roll and which can more easily be removed and changed in the event of damage or fouling. Such a system is also advantageous for products which may, for any reason, require frequent pattern changes.
Systems having non-integral elements are known. These systems are most frequently used in print technology, but have expanded over time to include embossing systems. The prior art embossing systems typically include a holding roll and a carrier for the emboss pattern. The carrier for the emboss pattern can take several configurations, the most common of which are sleeves, flexible plates or saddles.
A sleeve completely encircles the embossing roll and thus, suffers from a number of the drawbacks discussed above, including, for example, expense and difficulty in changing. The flexible plate and saddle configurations address the drawbacks of engraved rolls and sleeves by using a flexible plate or an inflexible curved plate (saddle) that does not completely encase the embossing roll.
Systems that use flexible plates or saddles are known to have two basic attachment configurations. The first is a mechanical system whereby the embossing plates or saddles are mechanically mounted to a holding roll, see for example, U.S. Pat. Nos. 3,646,886 and 3,603,256. Mechanically attaching a flexible emboss plate directly to the roll suffers from a number of disadvantages. These disadvantages include difficulty in changing the embossing plates due to space limitations between the roll and the attachment means. Further, the mechanical attachment means has to be configured so that it does not show or does not interfere with the embossing pattern.
Due to problems associated with mechanically attaching an embossing plate to an embossing roll, one solution has been to use a saddle and slug configuration. The saddle is an inflexible curved plate that carries a single slug. The slug is an engraved plate that carries the desired embossing pattern. The slug is mounted onto the saddle and thus, mechanical attachment means can be more easily configured so that they do not interfere with the embossing pattern.
The second system improves upon the ease of the mechanical system by using a magnetic holding system. This type of system is exemplified in U.S. Pat. No. 4,116,594. Most magnetic systems use a series of flexible plates that are directly mounted to the embossing roll. Magnetic systems are believed to have two advantages over the mechanical system: (1) the ease with which the embossing plates or saddles can be removed and replaced, and (2) the ability to cover the entire surface of the embossing roll to creating a continuous pattern which is not interrupted due to space for mechanical attachment means.
While both prior systems have had limited success, none of the systems provides a truly easy means for changing the saddles or flexible plates. In the mechanical systems, the plates must be removed and replaced which, depending upon the complexity of the hold mechanism, can cause significant down time for the converting line. Furthermore, even if a saddle/slug configuration were used, if more than a single slug and saddle were used, each slugs and saddle had to aligned both vertically and horizontally. In the magnetic systems, while the saddles or plates could be more easily removed, if more than a single plate or saddle were removed, replacement of the plates results in alignment problems that could result in significant down time for the converting line.
The present invention addresses these problems by providing a single unitary saddle that can hold one or more embossing slugs, thus providing a simple mechanical holding means that can be as easy to change as prior magnetically held plates without the concomitant problems associated with alignment. Such a system allows the slugs to be aligned off the embossing machine, while the system is still in operation. Once the converting line is stopped, the saddle can be quickly removed and a new saddle quickly added. The unitary saddle of the present invention can then be adjusted horizontally and vertically, while maintaining the relative arrangement of the slugs that carry the emboss patterns. The system according to the present invention allows for embossing slugs which are sized to cover the entire web surface with a continuous pattern or which are discrete elements that can be used to create registered patterns, for example, logos.
Further advantages of the invention will be set forth in part in the description which follows and in part will be apparent from the description or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.